The present invention is generally directed to a storage pod for storing work-in-process in a machine in a location readily accessible to an operator of the machine. The present invention is more particularly directed to an improved machine having a storage pod for storing work-in-process such as semiconductor wafers and providing a laminar flow of air through the storage pod and across the semiconductor wafers.
Semiconductor wafers are generally fabricated in a plurality of processing steps. These processing steps may include, for example, deposition of layers such as photoresist, ion implantation, diffusion, and etching. Each of these steps occurs in a different piece of processing equipment, known as a tool, such as an etcher or a furnace.
Between these processing steps, the semiconductor wafers are transported from one tool to another. The wafers are generally maintained in a storage device known as a cassette. The cassette may be a rack or frame which supports a number of wafers, for example 25 wafers. The cassette contacts only the edges of the wafers and maintains them in non-touching relation.
An important goal in transportation and storage of semiconductor wafers is prevention of contamination and damage to the wafers. Therefore, wafers are preferably maintained in an environment having an extremely low atmospheric particulate concentration. For example, processing equipment generally is kept in a clean room, which may be a class 10 clean room, meaning there are fewer than 10 particles 0.5 micron or larger in size per cubic meter of clean room air. Localized processing areas, including the tools where processing steps occur within the clean room, may have even lower particulate counts. Some areas may be, for example, class 1 areas. Particulate counts may be decreased in these areas by providing a laminar flow of filtered air through the area. It is desirable to store and transport wafers in the cleanest environment possible to reduce the risk of contamination.
Between processing steps, semiconductor wafers have heretofore been stored on shelves or in racks within the clean room. The shelves or racks have been located on the floor in the clean room or in the aisles between processing equipment. Storing work-in-process in this manner is inconvenient, since an operator seeking to move wafers between a processing tool and the storage area must physically carry the wafers, including the cassette or other storage device, the distance between the storage area and the tool. In addition to the inconvenience, this handling increases the likelihood of wafer damage or contamination. Moreover, storage of wafers in aisles adjacent to operator walkways and work areas also increases the risk of wafer damage and contamination, for example by inadvertent jostling of a storage rack by a passing operator.
When transporting semiconductor wafers between work areas, and between storage areas and work areas, the wafers have heretofore been stored in storage containers such as wafer boxes. These prior art wafer boxes have included a hinged top or lid which may be latched to secure a plurality of wafers carried on one or more wafer cassettes within the wafer box. The top or lid includes a handle for carrying the wafer box between work and storage areas.
Such prior art wafer storage containers have exhibited several limitations. Because the wafers or wafer cassettes stored within the container are accessible only by opening the top or lid and lifting the wafers or cassettes vertically out of the container, the container may only be used on an open shelf. The shelf must have sufficient vertical clearance above the container to allow the lid to open and the wafers or cassettes to be withdrawn or inserted. In addition, the vertical motion of withdrawing or inserting wafers or cassettes in the container from above may be ergonomically difficult for an operator transferring wafers or cassettes between a work area and the container.
Moreover, including a carrying handle on the top or lid of the storage container creates additional ergonomic problems for an operator transporting the storage container. A wafer storage container holding wafers and wafer cassettes may weigh 10-20 pounds. A single handle on the lid of the container requires that the container be carried in a single hand, putting great stress on the operator's arm, shoulder and back. In addition, supporting the entire container and its contents by a handle connected to the hinged lid requires that the hinges and latches which couple the lid to the body of the container support the entire weight of the container and its contents. This has required heavy duty hinges, latches and other hardware.
Accordingly, there is a need in the art for a work-in-process storage pod which minimizes the risk of wafer damage or contamination. There is a further need in the art for a wafer storage pod which is readily accessible, so as to be ergonomically accommodating, to operators loading and unloading work-in-process in a processing tool. There is a still further need in the art for a work-in-process storage container which is ergonomically accommodating to operators transporting the container and loading and unloading work-in-process in the container.